For unknown reasons, the incidence of allergies and asthma continues to increase in the US. It is increasingly clear that asthma is a heterogeneous disease with differing endotypes which suggest discrete pathophysiology. In humans, asthma exists in allergic and non-allergic forms. It is an unmet need in the field to better understand ho different mechanisms contribute to asthma endotypes. Genome wide array analysis has identified many asthma relevant genes. However, due to poor correlation between steady state mRNA levels and protein, transcriptomic approaches may overlook critical genes. Posttranscriptional gene regulation by RNA binding proteins (RBPs) and microRNAs (miRNAs) are increasingly recognized as important control mechanisms for proinflammatory genes. RBPs, such as HuR (elav1) which bind to AU-rich elements (AREs) play critical roles in coordinately regulating proinflammatory genes in asthma by stabilizing target gene mRNAs and increasing translatability. Methods used by our lab and others, called RNA immunoprecipitation applied to microarrays (RIP-Chip) have identified how RBPs are coordinately regulating inflammation. Posttranscriptional gene regulation plays an important role in CD4+ T differentiation, yet these processes are poorly understood. Our long term goal is to understand posttranscriptional gene regulation in airway inflammation. The objective of this application, which is our next step in pursuit of that goal, is to understand how HuR is regulating key molecules, such as Th2/Th17 cytokines and IL-2 during allergen challenge. The central esis is that the RBP, HuR, is permissive for development of CD4+ Th2 mediated allergic airway inflammation and required for normal IL-2 homeostatic expression. The rationale for this proposal is that our work has demonstrated that HuR controls both Th2 and Th17 differentiation. HuR KO mice do not develop airway inflammation due to suppression of Th2 cytokine production and do not have the ability to turn off IL-2 expression following T cell activation. Understanding posttranscriptional mechanisms of IL-2 and Th2/Th17 cytokine gene regulation will allow the field to modulate and affect outcomes of inflammatory responses in allergen driven asthma and also perhaps aid in better defining the heterogeneity amongst asthma endotypes. We plan to test the central esis and accomplish these objectives by the following four specific aims: 1) Does HuR ablation alter CD4+ Th subset differentiation?; 2) Determine whether HuR is required for allergic airway inflammation in vivo; 3) Mechanistic determinants of IL-2 and Th2 cytokine expression; 4) Determine whether human lymphocytes have dysregulated HuR expression. We believe our study is innovative, because such approaches will provide novel mechanistic insights into T cell posttranscriptional cytokine regulation. The proposed research is significant, because it will elucidate how airway responses connect at the molecular level with both adaptive and innate immunity to control lung inflammation.